(a) Field of the Invention
This invention relates to a drive mechanism for a tractor, and in particular--but not exclusively--to a drive mechanism which when fitted to a tractor allows the tractor to be moved at relatively low speeds.
(b) Description of the Prior Art
Conventional agricultural tractors are at times fitted with machinery which is to moved at speeds slower than that continuously obtainable in the lowermost gear of the tractor: for instance trenching or other excavating machinery typically has to be advanced at speeds in the range of from 10 to 400 m/h, whereas the slowest continuous speed of the tractor when in bottom gear may be as fast as 2 km/h. To ensure proper operation of the machinery, the tractor has to be advanced step-wise, by frequently engaging the lowest gear and driving the tractor through a small distance.
In order to overcome the above-described problem, it is known to fit a tractor with a special gear-box, either to replace the standard gear-box or for insertion in the drive train from the standard gear-box to the driven axle, which special gear-box provides an extra reduction ratio, such as of 20:1 or even as much as 50:1. This solution is however very expensive to implement, and, for a contractor, may be most inconvenient for the trenching or other machinery cannot be transferred from one tractor to another, as required, but only between modified tractors. Moreover, the machinery probably will be used much less than the tractor, to which it may be fitted, so the service life of the machinery is longer than that of the tractor. These factors mean that several low speed special gear-boxes have to be purchased and fitted to several tractors to allow optimum use and life of one piece of machinery. It is a principal aim of this invention to provide a tractor drive mechanism which can be arranged to provide a relatively low drive speed, without the attendant disadvantages of using known low speed gear-box mechanisms, as just-described.